Roger Ullman, age 7, of San Francisco, California, for his question:

How cold is the water at the bottom of the ocean?

As a rule, well water is cool    cooler than the sunny streams flowing along the surface of the ground. Out in the wide ocean, the tossing waves may be warmed by the sun. But the sunbeams cannot pierce far below the surface of the sea. If you dive deep into the ocean, the water below tends to get colder and colder as you go down. Even in the tropics, deep sea divers have to wear special suits to keep out the cold. But the deep ocean floors are two miles, maybe five or six miles below the deepest diver.

You would expect the ocean waters to get colder and colder all the way down to the bottom. But this does not happen. In fact, the deepest ocean water never gets cold enough to freeze into solid ice. The surface water gets cooler as we go down    but it stops getting any chillier when it reaches a temperature of four degrees Centigrade. From a mile or so below the waves, right down to the deepest ocean bed, the water stays just a few degrees above the freezing point of water.